(1) Field of the Invention
The present invention relates to an alumina-silica resin additive. More particularly, the present invention relates to an additive which has a fine particle size and a definite particle shape and which gives good slip characteristic and anti-blocking property to a resin when it is incorporated in the resin, and process for the preparation of this resin additive.
(2) Description of the Prior Art
When shaped resin articles such as films and sheets are kept piled to one another, blocking is readily caused, and from oil, various inorganic additives have been incorporated into resins for imparting a slip characteristic to the resins.
It is known that zeolites are excellent in this property. For example, Japanese Patent Publication No. 16134/77 teaches that if a zeolite powder having an average particle size smaller than 20 microns is added in an amount of 0.01 to 5% by weight to polypropylene, the blocking resistance of a biaxially drawn polypropylene film can be improved. Furthermore, Japanese Patent Application Laid-Open Specification No. 34356/79 teaches that if an aluminosilicate of the zeolite crystal having an ion exchange capacity is incorporated in an amount of 0.01 to 10% by weight into a chlorine-containing polymer, the thermal stability is improved and improvement of the exterior lubricating property is attained as an additional advantage.
As described above, zeolite particles are excellent in a slip characteristic (external lubricating property) and an anti-blocking property to a shaped resin article. However, a zeolite contains considerable amounts of basic components such as sodium, potassium, calcium and magnesium components in the form of an aluminosilicate, and therefore, because of the presence of these basic components, the shaped resin article is colored with the lapse of time. Moreover, since a zeolite has an adsorbing property, especially a water-adsorbing property, blowing is caused when the zeolite is incorporated into a resin.
Japanese Patent Application Laid-Open Specification No. 213031/83 discloses an alumina-silica additive comprising cubic primary particles having an Al.sub.2 O.sub.3 SiO.sub.2 molar ratio of from 1/1.8 to 1/5 and having one side smaller than 5 microns, wherein said particles are X-ray diffractometrically substantially amorphous and a BET specific surface area smaller than 100 m.sup.2 /g. It also is taught that the alumina-silica cubic particles can be prepared by acid-treating a crystalline zeolite having a cubic particle shape under such conditions that the crystallinity is substantially lost but the particle shape is not marred, and that cubic particles having such a particle size distribution that the content of particles having a size smaller than 10 .mu. is at least 98% by weight and particles having a size of 1 to 5 .mu. occupy at least 70% by weight of the total particles are preferred.
Various problems which arise when zeolite particles are incorporated into resins are solved by amorphous alumina-silica particles formed by the acid treatment of a zeolite. However, in the use where a thin thickness is required, for example, when this additive is used for a household wrapping material or a base film of a magnetic tape, the particles are too coarse. Accordingly, development of an additive for imparting an excellent slip characteristic and an excellent blocking resistance, which has a fine particle size and an excellent dispersibility in a resin, is desired.
However, if the zeolite to be subjected to the acid treatment is finely divided, the regular cubic shape of primary particles of the zeolite is destroyed during the acid treatment and the primary particles come to have an indeterminate shape. Furthermore, these indeterminate primary particles are agglomerated to form coarse particles.